1. Field of the Invention
This invention relates to optical sensing systems for measuring physical quantities and, more particularly, to a multi-channel optical sensing system for optically measuring physical quantities such as temperature and strain at a plurality of locations within a motor or a generator.
2. Description of the Prior Art
As the system for measuring a physical quantity, electrical sensing systems are well known and have been generally used. In such a system, a physical quantity to be measured is converted by a sensing element, which is provided at a measuring point and senses the physical quantity, into a corresponding electric signal which is transferred through a signal line to a measuring unit for analyzing the physical quantity. For example, in a system for measuring the temperature of the rotor of a generator during the operation thereof, thermistors, as temperature-sensing elements, are burried in the rotor at certain measuring points thereof, and signal lines which are electrically connected to the respective thermistors are led to and electrically connected to a slip ring, which is provided on the rotor, and through which detected signals from the sensors are supplied to a measuring unit provided at a location remote from the generator. These systems, however, have some problems. For example, since the detected signal is transferred through the slip ring, the transfer of the signal is unreliable. Also, since mechanical contacts are involved in the transfer of the signal, the service life is limited, and unreliable. Further, where thermistors are assembled within a generator, a signal having a high S/N ratio cannot be obtained due to the influence of strong electric fields and magnetic fields within the generator in which the thermistors is disposed. Furthermore, dielectric breakdown is likely to be caused by the strong electric fields.
There are also optical sensing systems for measuring the temperature. For example, a system using an infrared radiation thermometer detector for measuring the temperature of an apparatus such as a generator by detecting infrared rays emitted from the apparatus is well known in the art. With this system, in which the infrared detector and generator need not be electrically or mechanically coupled together, it is possible to solve the afore-mentioned problems. However, in case of a generator, in which the gap between the rotor and stator is small, typically 1 to 2 mm, difficulties are encountered in the measurement of infrared rays leaking from such a narrow gap at some measuring points in the rotor, particularly in the inner area in the generator, thus imposing restrictions upon the accuracy of the measurement.